As the semiconductor technology develops, it is desirable to scale down semiconductor devices to improve integration while reducing power consumption thereof. To reduce the power consumption due to current leakage, UTBB (ultra-thin buried oxide body) devices formed in semiconductor substrates are proposed. The UTBB device comprises an ultra-thin buried oxide layer disposed in the semiconductor substrate, a front gate stack and source/drain regions above the ultra-thin buried oxide layer, and a back gate beneath the ultra-thin buried oxide layer. In operation, a bias may be applied to the back gate to significantly reduce the power consumption while maintaining an operation speed unchanged. At present, it is difficult to apply the UTBB technology to fin-type Flash devices.